Pressure transducer

ABSTRACT

A pressure transducer having a thin, edge-supported lightreflecting membrane or membranes with light-transmitting optical fibers for directing collimated light to the membrane for reflection thereby. A plurality of light-receiving optical fibers are disposed around each light-transmitting fiber and are connected to a light intensity measuring device. Upon membrane deflection, the direction of light reflected therefrom is changed, thereby changing the amount of light incident on the light-receiving fibers. The resultant change in light intensity transmitted to the measuring device serves as a measure of the membrane deflection and therefore the pressure acting thereon.

. k l A, 0 3 9 ea 6 use 1 WOW O i v. m tates mre FOR W [H] 3580082 mimel'llzullzll N12}? XR [72] inventor Richar 11Strack [56] References CitedSturbridge, Mm UNlTED STATES PATENTS Q 5 $321 7 3,273,447 9/1966 Frank350/295ux Division ofserl Nu 6735780CL 9 1967' 3,387,494 6/1968 Golay73/406 P N 3 5011 1 Man 31, 1970 Primary ExaminerD0nald O. Woodiel [45]Patented May 25, 1971 Attorney-Stowe" and Stowell [73] Assignee TheBendix Corporation Detroit, Mich.

- ABSTRACT: A pressure transducer having a thin, edge-supportedlight-reflecting membrane or membranes with lighttransmitting opticalfibers for directing collimated light to the membrane for reflectionthereby. A pluralityoflight-receiving [54] PRESSURE TRANSDUCER opticalfibers are disposed around each light-transmitting fiber 9 Claims 7Drawing Figs and are connected to a light lfltfiilSllXfllfifiSUflngdevice. Upon membrane deflection, the dlrection of light reflected [52]U.S. Cl 73/406, therefrom is changed, thereby changing the amount oflight in- 350/295 cident on the light-receiving fibers. The resultantchange in [51] Int. Cl G011 7/08 light intensity transmitted to themeasuring device serves as a measure of the membrane deflection andtherefore the pres- [50] Field of Search...

406, 408; 350/295 sure acting thereon.

PRESSURE TRANSDUCER This application is a division of my applicationSer. No. 673,578 filed Oct. 9, I967. The transducer is fabricated bydepositing a thin coating of light reflecting material on a flat,polished surface of a substrate consisting of a mosaic comprising aglass core or cores encased by a glass casing or matrix of differentetching properties than the glass cores. After coating the core or coresare removed from the substrate by etching to furnish an edge-supportedmembrane or membranes consisting of residual coating in the area fromwhich the cores are removed. The light trans-- BACKGROUND OF THEINVENTION This invention relates generally to pressure transducers and,

more particularly, to a flexible diaphragm pressure transducer utilizinglight reflected therefrom to measure the deflection and therefore thepressure acting thereon.

Pressure transducers of the general type to which this inventionpertains are known in the art and generally consist ofthinfilm diaphragmhaving a reflective surface thereto. The diaphragm generally comprise anelastic member mechanically fonned by extrusion, calendering or likeprocesses. The reflective surface is usually in the form of a coatingformed on the diaphragm. A source of light is provided to transmit lightto the diaphragm for reflection thereby. Means are provided fordirecting light reflected from the diaphragm to a device such, forexample, as a photodetector, to convert the motion of the diaphragm tosound, electrical impulses, or other similar recording meansthrough the'brightness fluctuations caused by the change in intensity ofthereflected light.

Transducers such as these find great utility in systems for measuringpressure differences or fluctuations, high sensitivity microphones foruses such as listening devices and the like.

The prior art devices have heretofore been limited in sensitivity by thephysical limitations of membranes, reflective coating thickness, andcost of fabrication.

Because of mechanical formation of the diaphragm, the attainment ofsuitable thinness for high sensitivity and consistent property over thesurface area thereof has been relatively costly. The additionalthickness required by the coating of reflective material has provided afurther handicap insofar as high sensitivity is concerned. Furthermore,due to the nature of formation of the diaphragm and reflective surface,the cho' ice of materials available has been limited to those which maybe readily worked by the prior art methods.

SUMMARY OF THE INVENTION This invention provides a novel pressuretransducer which avoids the disadvantages of the prior art by providinga relatively simple and inexpensive means to form a thin pressuresensitive diaphragm greatly improved over the prior art devices.

The invention also provides a device wherein a highly sensitive multiplemembrane pressure transducer may be fabricated at minimal cost andcomplexity by utilizing fiber optic techniques in the fabricationthereof.

The invention further provides a novel method of fabricating a pressuretransducer with a thin combination diaphragmreflective surface formedhomogeneously by furnishing means to form a diaphragm of vitreousmaterial.

In a preferred embodiment, the invention consists of forming a substratefrom transverse wafers sliced from a matrixbound bundle of opticalfibers with etching properties different than the matrix produced inaccordance with complex fiber optic methods. A thin coating is formed ona polished surface of the matrix and the fibers are etched therefrom, toprovide free standing membranes at the points where the fibers areremoved from the support ofthe coating. Bundles of fibers are removedfrom the support of the coating. Bundles of fibers comprising alight-transmitting fiber surrounded by light receiving fibers arecentered in each recess left by removal of the fibers and light isdirected onto the membranes for reflection thereby. Light-sensing meansare connected to the lightreceiving fibers and deflection of themembrane under pressure is sensed by monitoring the quantity of lighttransmitted to the sensing device through the light-receiving fibers asthe angle of reflection changes with deflection of the membrane.

These and other objects of the invention will become better understoodby those skilled in the art by reference to the following detaileddescription wherein like components throughout the figures thereof areindicated by like numerals and wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevational sectionalview through a device comprising a single cell in accordance with theinvention during a preliminary stage of fabrication thereof;

FIG 2 is a sectional view of the cell of FIG. I taken along the line 2-2thereof;

FIG. 3 is a view similar to FIG. 1 showing the cell of FIG. 1 duringanother phase in the fabrication thereof;

FIG. 4 is an enlarged view similar to FIG. 1, showing a completed cellin accordance with the invention;

FIG. 5 is a sectional view of the cell of FIG. 4 taken along the line5-5 thereof;

FIG. 6 is a view similar to FIG. 4 showing the cell thereof in anoperational phase; and

FIG. 7 is a reduced sectional view showing a device comprising multiplecells in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As employed hereinafter, theterm glass" is used in its generic-sense and is intended to include allinorganic vitreous compositions and, where applicable, other materialshaving similar properties for the purposes set forth.

In FIGS. 1 and 2, an initial substrate, indicated generally at 10,comprises a glass core 12 encased in a glass cladding 14. Although theillustration of FIG. 1 is directed to a single cell, it is contemplatedthat the substrate 10 can also comprise a plurality of adjacent coresinterconnected by cladding prepared, for example, by the methoddisclosed in US. Pat. No. 3,294,504 issued Dec. 27, 2966 to Hicks. Inthat patent, a highly etchable glass rod is clad with a glass tubehaving a lower rate of etching than the rod. The cladding isaccomplished by drawing the rod and tube progressively through a heatedzone to form a composite fiber. For single-cell devices, the compositefibers may be cut transversely into .wafers to form the substrate withthe rod forming the core 12 and the tube forming the cladding 14. Formultiple-cell substrates, the composite fiber is cut, stacked and, ifsmaller diameter fibers are desired, redrawn through heated zones toform a multiple fiber of the required fiber density fused together by amatrix formed by the tubes. The redrawn multiple fibers are then cuttransversely in predetermined lengths, stacked upon one another, and thestacked multiple fibers are placed in, for example, metal molds having amovable mold surface, heated to the fusing temperature, and pressed intoa composite assembly. The stacked and fused multiple fiber unit is thensliced transversely across the fibers into wafers, and the resultantwafers form the multiple cell substrate of this invention, with thefibers forming the cores l2 and the matrix forming the cladding 14.

The transverse surface 15 of the substrate 10 thus produced is polishedby means known in the optics art to a high surface finish.

The glass constituents making up the cores I2 and the cladding I4 areselected from glasses having different etching properties, so thatportions of the substrate may be removed by selective etching thereof.For example, the fibers which ultimately form the cores 12 may compriseone of the lanthanum silicate glasses which are readily chemicallyetched Parfait with nitric acid. A suitable lanthanum silicate glass forthis 5 by weight purpose can comprise the following: 1

Percent SiO s 44. 9 I y W g t Na O -t- K 0 8BPitjjiii::::::::-::::::::::::;:;:: i? no 46.6 13203 18 (b): Th0 02 43.3 M0,, 10 9-? 2 0 Iron and alumlnumvoxldes 3 Pbo U 3 6 A glass notetched by nitric acid and suitable for the i5 9' f cladding 14 cancomprise, for exam le; 3

. Percent weight The coat ng can comprise glasses having the followingtypi- 9) n 80. 6 cal compositions (percent by weight).

2 a 13 g g W a8 12 IM0 0. 4 K20 O 6 A1203 2 2 (3 ,0 5 2 I MgO 3. 6

Although glass is specifically referred to hereinabove as the A1 0 1material making up the constituents of the substrate 10, various othermaterials having different etching properties may be EaCh 0f the fibers2 nd 24 n f rth r comprise bundles used if so desired. For some uses,however, it is essential that of the aforedescribed sihgle'ciad fibersformed as a unit y the constituents have all the characteristics ofpolished glass, h g the Cladding 35 further dlescl'ibed in hiatier'meflthat is,-an extremely smooth surface finish which is flatboth in honed Patent, 0r h P slhgie hh as 15 dictated y h microscopic dmacroscopic Sense, O i 1 flatness the particular use, size, andcharacteristics of the device for specifications such, for example, asfringe count etc. may which the IHVQhIiOh is ihtehdgd- The fibers 22 h24 are thereby be applied to the surface finish Additionally, on apreferably flexlble for purposes to be described in greater microscopicand submicroscopic scale, the surface detali belOW- smoothness withglass is of a much higher quality than would The fibers 26 servePnmanlyto fix and mechamcahy center be possible with any metal, plastic, orother nonvitreous subthfl? fibers 22 and m the recess 17. Means, otherthan the stance, fibers 26, can be utilized for this purpose if sodesired.

With the substrate 20 prepared as set forth'above, the In a preferredmethod of fabrication, the bundle 20 is inpolished surface 15 is coatedto form a supported membrane tl'OdUCCI ilttO the cell 18 as follows;Utilizing the above- 16 (FIG, 3). The specific processes of coating andthe various 4() described technique. the fibers 24 and 26 a formed as amaterials which may be utilized are described in greater detail uit, undby a matriX of material having different in copending application ofWilliam L. Gardner, Ser. No. filed etching properties than the materialof the aforedescribed v d t h ith, mitted FABRICATING THIN FILMS fibers.In this instance, the spaces formed between the various AND MEMBRANES, Fhe ur ofthi i venti the fibers as seen in FIG. 5 would initiallycomprise the binding membrane 16 is formed of a substance havingsuitable lightmatrix for the f s. Th C nduit is th n Cut to length andthe reflecting properties, preferably from a glass r vit ends thereofsuitable finished by optical polishing techniques material havingetching properties simil to th f h and inserted into the recess 17 ofthe cell 18 in spaced relamaterial of the cladding l4, e.g., resistantto etching by nitric tionship to the membrane 16 as seen in FIG. 4. Theinserted acid. The glass is preferably deposited on the substrate 10 byportion conduit is then fused or otherwise adhered to the cell utilizinga radiofrequency plasma sputtering unit in ac- 18 and the matrix isdissolved by etching externally of the cell cordance with a newlyimproved technique described in the aforesaid copending application.

After depositing the coating 16 to the thickness desired for theapplication or use to which the device is to be put, the core 12 (FIG.I) is removed by etching, thereby forming the cell, indicated generallyat 18, shown in FIG. 3, which'compn'ses the cladding 14 disposed in asupporting relationship to the coating 16 which now comprises afree-standing membrane over a recess 17 formed by removal ofthe core.

Referring now more particularly to FIGS. 4 and 5, a bundle of glassfibers, shown generally at 20, is connected to the cell 18. The bundlecomprises a centrally located first light transmitting optical fiber 22surrounded by a plurality of reflected light receiving or second opticalfibers 24 which are, in turn, further surrounded by a plurality of thirdfibers 26 (remaining portions shown in the FIG.) connecting the bundleto the walls of the recess l7. As best seen in FIG. 4, theabove-described fibers terminate in the cell 18 at a point spaced fromthe surface of the membrane 1650 that the membrane may deflect under theinfluence of pressure.

The fibers 22 and 24 are fabricated in accordance with methods known inthe fiber art and preferably methods such as that disclosed in US. Pat.No. 3,l46,-O82, issued Aug. 25, 1964, to Hicks. In that patent, a glassrod is provided with a glass coating having a lower index of refractionthan that of the rod. As set forth in that specification, compositionssuitable for the high index of refraction glass rods are as follows(percentages by weight):

leaving the individual fibers free. The fibers are then segregatedaccording to their size and the extending portions of the fibers 26 arecut away as seen in FIG. 4. The light-transmitting fiber 22 is connectedto a source of external light for transmission of collimated light tothe membrane as shown by arrows in FIG. 4. The fibers 24 are connectedto a light-detecting device (not shown) for conversion of light signalstransmitted therethrough into a displayable form. The display may beconverted, for example, into an audible state or may be calibrateddirectly in terms of pressure, or simultaneously, the pressure and soundmay be monitored.

In operation, collimated light is transmitted by the fiber 22 forreflection from the membrane 16. In FIG. 4, with the membraneundeflected in the absence of pressure, the light is reflected, asindicated by the arrows, directly back into the fiber 22. Light pickedup and transmitted by the fibers 24 is at a minimum, thereby generatinga'minimum signal at zero pressure conditions.

Referring now to FIG. 6 of the drawings, pressure acting on the membrane16 deflects it upwardly. In this condition, light transmitted throughthe fiber 22 is reflected from the convex surface, formed by thedeflected membrane 16, outwardly toward the fibers 24 as indicated bythe arrows. The reflected light is then transmitted through the fibers24 to the light-detecting device, the intensity thereof corresponding tothe deflection of the diaphragm, thereby providing an indication of thepressure, intensity and/or a continuing indication of varying pressurevalues according to the level of light received by the sensing device.

Referring to FIG. 7, a plurality of cells 180 through 18d are shown in amulticell transducer indicated generally at 28. This cell is preferablyformed in accordance with the complex glass fiber techniques set forthin the above description of the substrate fonnation. In thisarrangement, the respective fibers 220 through 22d can be connected tosingle or multiple sources of light, as desired. The fibers 240 through24d may be connected to single or multiple light detecting devices. Inthe former case, with a single light detecting device, the pressure overa large area may be sensed and/or averaged while, in the latter case,the pressure profile over an area can be monitored.

Refinements in the sensitivity of the device are possible by alteringthe basic light conveying mechanism by means such, for example, asaltering the angle of introduction and pickup oflight from the membrane16.

What has been set forth above is intended primarily as exemplary toenable those skilled in the art in the practice of the invention. Itshould, therefore, be understood that, within the scope ofthe appendedclaims, the invention may be practiced other than specificallydescribed. What is new and therefore desired to be protected by LettersPatent of the U.S. is:

I claim:

l. A pressure transducer comprising:

a diaphragm means formed by depositing a coating of lightreflectingmaterial on a flat surface of a cored matrix and subsequently removingthe core to produce at least one edge supported membrane consisting ofthe portion of said coating spanning the opening left by removal of thecore;

light-transmitting means mounted in said opening in spaced relation tosaid membrane to deliver collimated light to said membrane forreflection thereby;

light-sensing means including means disposed adjacentsaidlight-transmitting means to receive light reflected from said membrane;and

whereby, upon deformation of said membrane by pressure,

light reflected thereby is deflected, thereby varying the light incidenton said light sensing means. 2. A pressure transducer comprising: asource of collimated light; an edge-supported diaphragm means includinga pressure sensitive light-reflecting membrane; light-transmitting meansincluding at least one first lighttransmitting optical fiber fortransmitting said light to said membrane and disposed to terminate inspaced relation to said membranej light-sensing means including meansdisposed adjacent said light-transmitting means to receive lightreflected from said membrane; and

said membrane being constructed and arranged to reflect substantiallyall the light to said first fiber when undistorted and to reflect lightto said light-sensing means in direct proportion to the distortion ofsaid membrane by pressure.

3. A device in accordance with claim 2 wherein said sensing meansincludes at least one second light-transmitting optica fiber disposedadjacent to said first fiber.

4. A device in accordance with claim 3 wherein said first fiber iscentrally located with respect to said membrane and said second fibersare disposed around the periphery of said 5. A device in accordance withclaim 4 wherein said diaphragm means further includes at least onetubular cell disposed normal to and supporting said membrane.

6. A device in accordance with claim 5 wherein a plurality of thirdfibers are disposed between said second fibers and the walls of saidcell to centrally locate and support said first fiber and said secondfibers therein.

7. A device in accordance with claim 6 wherein said membrane is formedof vitreous material.

8. A device in accordance with claim 7 wherein at least said first andsecond fibers are flexible.

9. A device in accordance with claim 8 wherein said membrane issupported by a plurality of tubular cells and wherein first, second andthird fibers are provided for each of .said cells.

1. A pressure transducer comprising: a diaphragm means formed bydepositing a coating of lightreflecting material on a flat surface of acored matrix and subsequently removing the core to produce at least oneedge supported membrane consisting of the portion of said coatingspanning the opening left by removal of the core; light-transmittingmeans mounted in said opening in spaced relation to said membrane todeliver collimated light to said membrane for reflection thereby;light-sensing means including means disposed adjacent saidlight-transmitting means to receive light reflected from said membrane;and whereby, upon deformation of said membrane by pressure, lightreflected thereby is deflected, thereby varying the light incident onsaid light sensing means.
 2. A pressure transducer comprising: a sourceof collimated light; an edge-supported diaphragm means including apressure sensitive light-reflecting membrane; light-transmitting meansincluding at least one first light-transmitting optical fiber fortransmitting said light to said membrane and disposed to terminate inspaced relation to said membrane; light-sensing means including meansdisposed adjacent said light-transmitting means to receive lightreflected from said membrane; and said membrane being constructed andarranged to reflect substantially all the light to said first fiber whenundistorted and to reflect light to said light-sensing means in directproportion to the distortion of said membrane by pressure.
 3. A devicein accordance with claim 2 wherein said sensing means includes at leastone second light-transmitting optical fiber disposed adjacent to saidfirst fiber.
 4. A device in accordance with claim 3 wherein said firstfiber is centrally located with respect to said membrane and said secondfibers are disposed around the periphery of said first fiber.
 5. Adevice in accordance with claim 4 wherein said diaphragm means furtherincludes at least one tubular cell disposed normal to and supportingsaid membrane.
 6. A device in accordance with claim 5 wherein aplurality of third fibers are disposed between said second fibers andthe walls of said cell to centrally locate and support said first fiberand said second fibers therein.
 7. A device in accordance with claim 6wherein said membrane is formed of vitreous material.
 8. A device inaccordance with claim 7 wherein at least said first and second fibersare flexible.
 9. A device in accordance with claim 8 wherein saidmembrane is supported by a plurality of tubular cells and wherein first,second and third fibers are provided for each of said cells.